For many years, surgeons have employed needle-suture combinations in which a suture or ligature is attached to the shank end of a needle. Such needle-suture combinations are provided for a wide variety of monofilament and braided suture materials, both absorbable and non-absorbable, e.g., catgut, silk, nylon, polyester, polypropylene, linen, cotton, and absorbable synthetic materials such as polymers and copolymers of glycolic and lactic acid.
One typical method for securing a suture to a needle involves providing a cylindrical recess in the shank end of a needle and securing a suture therein. For example, U.S. Pat. No. 2,928,395 teaches the addition of an adhesive material to such a substantially cylindrical recess to secure the suture therein. Additional methods for bonding a suture within a needle bore are described in U.S. Pat. No. 3,394,704 (bonding agents). Alternatively, a suture may be secured within an axial bore in a needle by swaging the needle in the region of the recess. See, e.g., U.S. Pat. No. 1,250,114. Additional prior art methods for securing a suture within a needle bore include expansion of a catgut suture through the application of heat (U.S. Pat. No. 1,665,216), inclusion of protruding teeth within the axial bore to grasp an inserted suture (U.S. Pat. No. 1,678,361) and knotting the end of the suture to be inserted within the bore to secure the suture therein (U.S. Pat. No. 1,757,129).
Methods for detachably securing a suture to a needle are also well known. For example, U.S. Pat. Nos. 3,890,975 and 3,980,177 teach swaging a suture within a needle bore such that the suture has a pull-out value of 3 to 26 ounces. Martinez U.S. Pat. No. 4,127,133 also discloses the use of wax as a bonding agent for controlled release needles. Alternative detachable attachment methods include providing a weakened suture segment (U.S. Pat. No. 3,949,756), lubricant tipping the end of a suture to be inserted in the axial bore of a needle (U.S. Pat. No. 3,963,031) and pre-tensioning a suture that is swaged within an axial needle bore (U.S. Pat. No. 3,875,946). See also, U.S. Pat. Nos. 3,799,169; 3,880,167; 3,924,630, 3,926,194; 3,943,933; 3,981,307 and 4,124,027.
Another method for attaching a suture to a needle involves the use of tubing which is secured to the shank end of the needle and to the suture. For example, U.S. Pat. No. 1,613,206 describes the use of a tubing (preferably silver), which is secured to the shank end of a needle and to a ligature by pressure or cementing. It is also suggested that the shank of the needle be of reduced cross section and that the furthest extremity of the reduced diameter shank section be provided with a spike or point upon which the suture may be secured prior to tube application.
U.S. Pat. No. 2,240,330 describes a tubing attachment method whereby the tubing and suture are reasonably secured to the needle. In particular, the needle and tubing are provided with cooperating catch and abutment means which are released one from the other by rotating the needle 90.degree. relative to the tubing (or vice versa). The tubing is manufactured from spring-tempered carbon steel or chrome nickel steel and is secured to the suture by heating the tubing and then swaging to the suture.
U.S. Pat. No. 3,918,455 describes a needle-suture attachment wherein a hollow suture portion is secured to the shank end of a needle which is of reduced cross-section as compared to the remainder of the needle.
Additional patents which describe the use of tubing to effect suture-needled attachment include U.S. Pat. Nos. 4,672,734 (forming needle from U-shaped metal plate around suture), 4,359,053 (silicone tubing), 3,835,912 (laser welding of metal tube to needle), 2,814,296, 2,802,468 (chamfered tubing ends), 2,302,986, 2,240,330 1,981,651 (needle and tubing screw threaded), 1,960,117, and 1,591,021.
In addition to the needle-suture constructions of the afore described pull-out variety, it is known from U.S. Pat. No. 4,805,292 to provide a needle-suture combination in which a suture cutting edge is formed at the shank end of the needle. However, the combined needle-suture device of U.S. Pat. No. 4,805,292, like others described above, possesses a suture tip-receiving axial bore, or recess, formed in the butt end of the needle and as such is subject to the disadvantages recounted above which are associated with a needle possessing an axial bore.
Insertion of sutures into a hole, recess, or tube for attachment to surgical needles presents problems peculiar to suture needle combinations. Braided multifilament sutures in particular are difficult to inset into the very small aperture of a surgical needle; unless modified, they are too limp for the suture tip to be controlled for insertion and they have a tendency to "broom", i.e., the filaments have a tendency to flare out at the cut end so that the diameter of the cut end of the suture exceeds the diameter of the hole in the needle. Various techniques have been employed to modify sutures to overcome the problems of limpness and brooming. One known method employs a tipping agent, which is a material used to coat the suture to stiffen the filaments and adhere them together.
Typically, a suture to be tipped is first placed under tension to reduce slack so that the suture may be maintained in a predetermined position on a frame or rack or other suture holding device. Optionally, the tension may be such as to reduce the diameter of the suture. See Canadian Pat. No. 1,009,532. The suture is then dipped into the tipping solution and allowed to dry while under tension. The sutures are then dried, such as by being warmed in a drying oven at about 225.degree. F. for about 10 minutes. After drying the sutures can be cut and released from tension. The process results in a tipped end on each side of a cut. Where tension has optionally been employed to reduce the suture diameter, release of said tension will allow the suture to expand to its original diameter except at the tipped end portion. This can facilitate insertion of the end into a needle.
Tipping agents are dissolved in solvents to form dipping solutions. By way of example, Mariotte mixture is a dipping solution comprising nylon dissolved in isopropyl alcohol. Other polymers and solvents may also be used. Gould mixture is a dipping solution comprising nylon dissolved in methanol. At least one major manufacturer of surgical needles recommends use of Mariotte mixture or Gould mixture for tipping sutures. A multitude of other tipping agents, including a polymer and solvent, have been proposed. For example, McGregor U.S. Pat. No. 3,890,975 discloses coating the suture with a binding resin or adhesive. The composition may be any non-toxic adhesive composition, either organic, inorganic or a hybrid. Suitable organic materials are such natural products as starch, dextrin, asphalt, animal and vegetable proteins, natural rubber, shellac, semi-synthetic products such a cellulose nitrate and the other cellulosics, polyamides derived from dimer acids, castor-oil based polyurethanes; such well-known synthetic resins as vinyl-type addition polymers, both resins and elastomers; polyvinyl acetate, polyvinyl alcohol, acrylics, unsaturated polyesters, butadiene/acrylonitrile, butadiene/styrene, neoprene, butyl rubber, polyisobutylene; and polymers formed by condensation and other step-wise mechanisms, i.e. epoxies, polyurethanes, polysulfide rubbers, and the reaction products of formaldehyde with phenol, resorcinol, urea and melamine. McGregor states that particular preferred bonding compositions are epoxide resins and polyester resins.
Schmitt U.S. Pat. No., 3,736,546, discloses that it is known to tip braided sutures by dipping the end of the suture in a plastic such as a solution of nylon in isopropyl alcohol. Schmitt suggests that for absorbable sutures an absorbable tipping agent is desirable, and proposes that a copolymer of lactic and glycol acid dissolved in a suitable organic solvent, such as xylene or toluene, be applied to tip the suture.
Nichols U.S. Pat. No. 2,734,506 discloses a tipping solution of polymers of methacrylic acid esters in an organic solvent such as toluene, xylene acetone, ethyl acetate, methethyl ketone, or naphtha.
Shepherd et al. U.S. Pat. No. 3,849,185 discloses the use of an acrylic casting syrup as a tipping agent, the syrup being fully polymerized after being applied to the suture.
In addition, paraffin/hexane solution (10% paraffin) has been used as a suture coating agent as well as ArroChem (TM), a nylon resin plus methanol composition manufactured by ArroChem, Inc. of 201 Westland Farm Road, Mt. Holly, N.C. 28120, and SILASTIC (TM) Medical Adhesive (a silicon elastomer composition manufactured by Dow Corning Co.).
Although tipped sutures prepared in accordance with the above procedures may have been used successfully, there are several drawbacks with the use of tipping solutions. The main problems related to tipping consistency and process control. Non-uniform solvent evaporation, which may be caused by variants in the solvent, oven temperature and heating time can result in inconsistent tipping. Furthermore, the dried residue of polymer left after evaporation can flake off or develop cracks. Additionally, most tipping solvents used in tipping solutions are hazardous and presents significant handling and disposal problems.
Another method for tipping sutures is to heat treat the suture tip. Since the 1970's braided thermoplastic sutures have been tipped by placing the end of a suture in a heated die to consolidate the end and form a shaped tip that was suitable for insertion into a needle. The die could be heated with an electric resistance heater or an ultrasonic generator. Sutures can also be tipped by contacting a heated surface to a tensioned length of suture to form a stiffened region which will be subsequently cut to form two tips. Recently, Coates described a variation on this approach in U.S. Pat. Nos. 4,832,025, 5,226,336, and 4,806,737, which consisted of heating a tensioned length of suture in a radiantly heated tunnel followed by cutting the heat treated length of suture to form two tips. Sutures can also be heat tipped by placing a thermoplastic suture on a rack or frame under tension and dipping the portion to be tipped into a hot inert fluid. The portion of the suture inserted into the inert fluid will be heat set or drawn (depending on the suture material, tension, the temperature of the fluid and the duration of the exposure to the heated fluid) and thereby stiffened. The suture may be removed from the rack or frame and the stiffened portion can be subsequently cut to form one or more suture tips. Unfortunately, using heat to melt a region of the suture may weaken the suture if not carefully controlled.
Thus, it would be a significant contribution to the art to tip sutures without using solvents or exposing the suture to high temperatures. It is, therefore, an object of the present invention to provide a process for tipping braided surgical ligatures on sutures that do not require the use of tipping solvents or high temperatures.